The present invention relates to the field of semiconductor integrated circuits. The invention is illustrated in an example with regard to a semiconductor integrated circuit wet processing method and apparatus, but it will be recognized by those of skill in other arts that the invention has a wider range of applicability. Merely by way of example, the invention can also be applied to the manufacture of raw wafers, disks and heads, flat panel displays, microelectronic masks, and other applications requiring high purity wet processing such as steps of rinsing, drying, and the like. The present invention generally relates to a nozzle and a method for dispensing process liquids onto a surface. More particularly, the present invention relates to a fluid dispense nozzle for dispensing fluids of photoresist developer chemicals, photoresist chemicals, cleaning and rinsing chemicals, etchant chemicals, or dielectric chemicals onto a rotating semiconductor substrate material.
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or xe2x80x9cwafer.xe2x80x9d The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Two very common families of photoresists are phenol-formaldehyde polymers and polyisoprene polymers.
Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as bio-aryldiazide and o-naphthaquinone-diazide, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing solvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers.
After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer. Common developers are tetramethyl ammonium hydroxide, sodium hydroxide, xylene and Stoddard solvent. After development rinsing is performed with fluids such as water or n-Butylacetate.
The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer.
Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Photoresist solution, developer solution and other process liquids are typically applied to the wafer using a spin coating technique in which the process liquid is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the liquid over the surface of the material. In particular, when developer chemicals are applied to the surface, it is necessary to quickly and gently produce a deep puddle of developer on the wafer to ensure that the photoresist layer is dissolved uniformly in areas that are soluble in the developer. In a developing process, among other manufacturing processes for a semiconductor device, a developer should be uniformly applied to a resist film on a semiconductor wafer within a predetermined time. The reason is that the developing uniformity for the resist film is generally supposed to depend on the state of development, so that the development is subject to irregularity unless the developer is first uniformly supplied to the whole surface of the wafer. Conventionally, therefore, liquid coating nozzles of various types have been proposed.
U.S. Pat. No. 4,267,212 discloses a process for spin coating a semiconductor wafer uniformly with a coating solution such as a photographic emulsion by rotating the wafer at a first speed while simultaneously applying the coating solution through a circular nozzle at a radially moving position. Once the semiconductor wafer has been initially covered, the speed of rotation of the wafer is increased and rotation continues until a uniform coating has been obtained. A similar process having a stationary nozzle is disclosed in U.S. Pat. No. 3,695,928.
In each of the aforedescribed apparatuses and methods, the fluid coating material is dispensed in a column of fluid whose cross-section approximates a circle, either during wafer rotation or while the wafer is stationary. Wafer coating is achieved by building up a pool of the fluid coating material in the nature of a thick layer and spin casting a film thereof by accelerating the rotation of the wafer about its own center in order to remove the excess material and to leave a thin film coating therebehind. The amount of fluid coating material, such as photoresist, remaining on the wafer is known to be a very small fraction of the amount that is initially dispensed, approximately one part in one thousand. This results in a substantial material loss of unusable photoresist along with its attendant cost. In addition, this creation of a pool of the fluid coating material on the wafer surface can result in the formation of uneven films which might adversely effect subsequent wafer processing.
Very specifically, in the prior art, a variety of devices, called nozzles, are used to apply fluids to a wafer surface. In FIG. 1, a simple spout nozzle 5 is depicted with an orifice 10 at the end of a spout attached to a fluid supply tube 15. The nozzle is positioned above the center of a rotating wafer 20 shown in the plan view.
FIG. 2 depicts a side view of this device dispensing fluid 31 onto the wafer 20 supported by a spin chuck 33 connected to a motor (not shown) that rotates the chuck and thus the wafer. In this nozzle 5, the fluid reaches the wafer center 35 first and only gradually is dispersed by centrifugal force to the perimeter 37 of the wafer. In fact, even after distribution to the perimeter, a greater amount of developer remains near the center 35 as shown in FIG. 3.
FIG. 4 depicts a cross-sectional view along a longitudinal axis of another version of the prior art, known as a block nozzle 55, which tries to solve some of the difficulties of the spout nozzle. In this case, the block nozzle 55 is a rectangular vessel 40 with an interior 42 serving as a liquid reservoir. The nozzle""s top surface 44 has two inlet fittings 46A, B for attachment to a fluid supply tube 48A, B, a support 41 for connection to an external apparatus not depicted, and an outlet fitting 43 for attachment to a gas outlet tube. The bottom 45 of the nozzle has a portion downwardly projecting called a nozzle tip 47 with a multiplicity of openings or orifices, e.g., 49, out of which the fluid is dispensed.
FIG. 5 depicts a transverse cross-section of the block nozzle 55. The figure shows the orifices, e.g. 49, in fluid communication with the vessel""s interior 42 through a slit 51 in the nozzle tip 47 and small passages 53 in the bottom wall of the interior. The nozzle tip and its orifices are arranged on the nozzle in a row approximately the diameter of the wafer, and each of the orifices have similar opening areas.
FIG. 6, in bottom plan view looking upwards from a rotating wafer 20 below the block nozzle 55, shows the block nozzle with its row of orifices 49A-I. A variation of the block nozzle is the partial-block nozzle 57 depicted in bottom plan view looking upwards from a rotating wafer 20 in FIG. 7. The difference between the block and partial-block nozzle is apparent by comparison to the wafer diameter. The partial-block nozzle is only about half the length of the block nozzle, and when placed over the wafer, extends about one wafer radial length from the center to the perimeter 59. The cross-sectional views of the partial-block nozzle 57, along both its longitudinal axis and its transverse axis, would be similar to the cross-sectional views of the block nozzle 55 shown in FIG. 4 and FIG. 5.
Unlike the spout nozzle, the block nozzle and partial-block nozzle dispense fluid near the perimeter 59 of the wafer and at points between the perimeter and center 52 at the same time that those two nozzles dispense fluid to the center of the wafer, thereby solving the most extreme difficulty of the spout nozzle. However, despite the improvement in uniform distribution of the dispensed fluid on the wafer, substantial non-uniformity persists.
To understand the cause of the persisting non-uniformity, suppose the wafer is 8 inches in diameter, suppose that the nozzle is of the partial-block design, and suppose that there are four equally-spaced orifices of equal opening area. Suppose further that in FIG. 7 the nozzle is placed so that one end orifice 54E overlies the center of the wafer 52, while the other end orifice 54A overlies a wafer region just inside the wafer""s perimeter 59. The first end orifice dispenses fluid onto the wafer""s center while each of the other three orifices dispenses fluid onto a separate annulus.
FIG. 8 shows a circular region 60 of one inch radius and three concentric annular regions 62, 64 and 66 of inner and outer radii, respectively, of 1xe2x80x3 and 2xe2x80x3, 2xe2x80x3 and 3xe2x80x3, and 3xe2x80x3 and 4xe2x80x3. The area of each annulus is xcfx80 (r2outerxe2x88x92r2inner) and, accordingly, FIG. 9 shows the area 61 of the 1xe2x80x3 circle 68 and the three successive annuluses as a function of the radius 63 of the circle and the outer radius of the three annuluses. From FIG. 9 it is evident that the area of the circle is {fraction (1/7)}th of the outer-most annulus. Accordingly, assuming approximately equal fluid flow per unit time through the opening of each orifice, the fluid dispensed from the central orifice 54E in FIG. 7 is spread over an area only {fraction (1/7)}th that of the fluid dispensed from the orifice nearest the wafer""s perimeter 54A. As a result, assuming for simplicity fluid dispensed over the circle 68 remains in the circle and fluid dispensed over the perimeter annulus 66 remains there, serious non-uniformity with a radial dependence exists because the average thickness of the dispensed fluid over the center circle is seven times that over the perimeter annulus. This non-uniformity will be further exaggerated as the semiconductor industry over time employs wafers of ever-increasing diameter. As a result, over-development can occur in the wafer center compared to the wafer perimeter.
The timing of the application of developer fluid to the wafer can also affect the uniformity of the results of development. For example, chemically amplified photoresists tend to develop much more rapidly than non-chemically amplified photoresists. The speed of chemically amplified photoresists can be as little as one second. That time is often less than the time required to apply the developing solution to the entire wafer surface. Consequently, if some portions of the wafer are covered with developer earlier than other portions, the developing process will proceed to a farther stage at those earlier portions in a given amount of time.
In the use of the partial-block design described in FIG. 7, the center circle 68 is covered with at least some fluid at the onset of fluid dispensing, while the perimeter annulus 66 receives fluid along its full extent only at the end of one revolution of the wafer spun by the chuck. Accordingly, if the fluid is developer, development begins much sooner on the center circle than at many portions of the wafer perimeter. That development might even run to completion much sooner at the central circle than in the perimeter annulus in the event chemically-amplified photoresists are used, for the reasons discussed above.
Accordingly, there is a need for a nozzle which applies fluid uniformly per unit wafer area to wafer portions of increasing distance from the center to produce more uniform thickness of the dispensed fluid over the whole wafer area and therefore more uniform photoresist layers and more uniform development processes.
Moreover, there is a need for more rapid application of the wafer fluid to wafer regions distant from the wafer center. That more rapid application will produce more uniform development times from the beginning of fluid dispensing independent of the distance of the wafer region from the wafer center.
Accordingly, there is an unsolved need for an apparatus which minimizes consumption of the coating material, such as photoresist, during spin casting and the like, as well as providing a more uniform and more rapidly applied thin film coating on semiconductor wafers during the fabrication of integrated circuits and other electronic components therefrom in the semiconductor industry.
Thus, it is apparent that a need exists for an improved nozzle for spin dispensing apparatuses which overcomes, among others, the above-discussed problems so as to produce a more uniform and more rapidly applied layer of process liquid over the surface of the wafer.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to a wedge-shaped nozzle for dispensing fluids onto a round surface with a generally uniform volume of fluid per unit area of the round surface to achieve rapidly a uniform thickness of applied fluid on the round surface. The wedge-shaped nozzle has orifices of equal size disposed on its bottom through which the fluid is dispensed. The orifices are disposed along arcs, with increasing numbers of orifices on the arcs at greater and greater distances of the arcs from the apex of the wedge-shaped nozzle. The numbers of the orifices on each arc are proportional to the area of an annular region determined by the arcs.
Accordingly, the present invention provides an improved nozzle that allows process liquid to be dispensed more uniformly on a rotating surface, which provides for a more uniform distribution of the process liquid on the surface of the layer, while requiring less process liquid and slower rotational speed to ensure full coverage of the surface.
One object of the present invention is to provide an apparatus for applying a thin layer of a fluid material such as photoresist or developer fluid on the surface of a wafer which eliminates pooling of the material.
Another object of the present invention is to provide an apparatus for applying a layer of a fluid material such as a photoresist or developer fluid on the surface of a wafer which reduces the amount of the material required for a given coating thickness.
Another object of the present invention is to provide an apparatus for applying a layer of a fluid material such as a photoresist or developer fluid on the surface of a wafer which enhances uniformity of coating thickness.
Another object of the present invention is to provide an apparatus which renders uniformity of fluid material application to a wafer more insensitive to greater and greater wafer diameters.
Another object of the present invention is to provide a photoresist application or developing treatment apparatus making it possible to form a resist pattern having a very small measurement error range and high precision and improve the yield rate of the resist pattern.
Another object of the invention is to provide a method for photoresist application or developing treatment making it possible to form a resist pattern having a very small measurement error range and high precision and improve the yield rate of the resist pattern.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinbefore. These and other details, objects, and advantages of the invention will become apparent as the following detailed description of the present preferred embodiment thereof proceeds.